In certain applications it is desirable to permit an internal combustion engine to operate while being controlled from a remote location. For such applications, prior art systems have been developed that permit a desired engine speed command to be communicated to a remotely located engine via a telephone line or other communication link. The remotely generated desired engine speed command is then used by the engine controller to control the engine speed. Such remote control is sometimes used to control equipment in isolated locations in connection with compressors and generator sets, among other applications.
Even a remotely controlled engine, however, must sometimes be controlled locally. For example, if maintenance must be performed on the engine (or on equipment associated with the engine), the maintenance technician must be able to start and stop the engine and control the engine speed while performing the maintenance. Generally, in prior art controls that permit such remote operation, there is a toggle switch on the control panel that indicates whether the control is using a local desired engine speed command or a remote desired engine speed command to control the engine. When the maintenance technician wants local control he or she simply moves the toggle switch to the local position. The engine control then uses a local desired engine speed command developed through a potentiometer or other device to control engine speed. Then, when the technician has finished performing the maintenance, he or she simply moves the switch back to the remote position and the control then passes the remote engine speed command to the engine controller. While this technique may work satisfactorily in some situations there are significant drawbacks. For example, if the remote engine speed signal is significantly greater than the local engine speed signal, abruptly shifting from local to remote mode could result in an engine speed surge. Likewise, shifting from remote operation to local operation can produce a similar surge. Such surges are undesirable and could create stress on the engine.
It would be preferable to have a speed control system that permits two engine speed command signals to be selectively used and that minimizes engine speed surges when changing from one speed command to the other. Thus, one object of the present invention to permit an operator to switch from local to remote mode without creating undue engine speed surges.